1. Field of the Invention
The present invention relates to a press machine such as a punch press or the like that can detect load acted on a frame.
2. Description of the Related Art
When a punch press performs press working, load is imposed on a frame of the punch press. When overload exceeding an allowable limit of the frame is imposed, each portion of the machine including the frame maybe damaged. When performing punch working, which is defined as press working, load required for such punch working can be estimated from the thickness of a work and from the size of a portion to be punched, however, when performing forming, it is difficult to estimate load required for such forming, and overload may be applied.
In order to prevent a machine abnormality resulted from overload, Patent Document 1 suggests to provide a drive transmission system arranged between a drive source and a punch tool of a press driving device with load detecting means such as a strain gauge or the like, and thus to output an abnormality signal when a detection value of the load detecting means exceeds a prescribed set value.    [Patent Document 1] Japanese Unexamined Patent Application Publication No. H8-19900
However, the aim of providing the drive transmission system with the load detecting means is not to measure the load actually acted on the frame. Accordingly, the load acted on the frame may not be detected precisely. Further, since the position of the load detecting means moves at the time of press working, it may be difficult to install wiring for acquiring the output of the load detecting means.